1. Field of the Invention
The present invention relates to a fabrication method for semiconductor materials, and in particular relates to a fabrication method for a chalcopyrite powder.
2. Description of the Related Art
Semiconductor materials have a special band gap which can be regulated by changing the composition of the semiconductor material. Therefore, semiconductor materials are often used as light absorbing layers of a photoelectronic device.
Among the different semiconductor materials used in CIGS solar cell, the Group IB-IIIA-VIA compound, which has a chalcopyrite structure, has been intensely researched. When a thin film made by the Group IB-IIIA-VIA compound is applied to a CIGS solar cell, good photoelectric conversion efficiency of the CIGS solar cell is obtained.
A thin film having the chalcopyrite compound is fabricated by a vacuumed or non-vacuumed process. The vacuum process comprises a co-evaporation or sputtering process. The non-vacuum process comprises an electrodeposition, electroless, coating or chemical spray pyrolysis process. Because, the vacuum process can only be applied to small-scale photoelectronic devices and equipment for the vacuum process is expensive, a non-vacuum process has been developed.
The conventional vacuum process is described as follows. Firstly, a precursor containing the Group IB and IIIA metal ions is deposited on a substrate. The precursor is then subjected to reduction and selenization processes at high temperatures to obtain a chalcopyrite compound. However, the Group IIIA metal has a low melting point, thus non-uniformed thin films are formed at high temperatures due to aggregation. As such, various fabrication methods for forming uniformed thin films with the chalcopyrite compound have been developed.
U.S. Pat. No. 5,445,847 discloses a fabrication method for a chalcopyrite compound. Firstly, a Group IB powder and an IIIA powder are mixed in a ball mill and sintered at a high temperature to obtain an IB-IIIA oxide. The IB-IIIA oxide is heated under gas containing Group VIA elements to obtain the chalcopyrite compound.
U.S. Pat. No. 6,268,014 also discloses a fabrication method for a chalcopyrite compound. The IB-IIIA oxide particles are first fabricated. Then, the IB-IIIA oxide particles are coated on a substrate by a spray process and are heated under the gas containing Group VIA elements to obtain the chalcopyrite compound.
However, both fabrication methods form non-uniformed thin films with the chalcopyrite compound. Accordingly, there is a need to develop a chalcopyrite powder which may be fabricated to form a uniform thin film with small size.